The aim of this investigation is to characterize the lumenal plasma membrane of the mammalian urinary bladder by methods of electron microscopy and biochemistry. Because of its distinctive morphology and relatively simple protein profile, this membrane, which can be isolated routinely in amounts of approximately 4 mg, serves as a model for determining normal plasma membrane structure and function and for understanding pathological membrane changes that occur when the epithelium becomes neoplastic. Experiments will deal with three areas: (1) Molecular architecture will be studied by defining the chemical nature of isolated membrane components, particularly the arrays of particles (plaques) that are characteristic of the lumenal membrane and can be separated from it. Disruption and reconstitution of membrane components will be attempted. Localization and orientation of membrane components will be explored by labeling experiments employing radioactive isotopes and labeled antibodies. (2) The structural role of membrane components, especially how the membrane is attached to cytoplasmic filaments and how plaque particles are linked together in the membrane, will be investigated. A procedure for isolating lumenal membranes with, as well as without, attached cytoplasmic filaments is being developed to allow (a) comparison of their polyacrylamide gel profiles prior to and following chemical, physical, and/or enzymatic disruption and (b) comparison of isolated membrane proteins with actin and spectrin in respect to their chemical, physical, and antigenic properties. (3) Surface characteristics of the lumenal membrane glycocalyx will be defined and experimental conditions leading to alterations in surface morphology will be determined and correlated with alterations in membrane impermeability under the same set of conditions.